1. Field of the Invention
The present invention relates to sensors which detect toxic or combustible gases by causing the dissociation of the gases into charged species such as ions and complex ions.
2. Description of the Prior Art
The prior art includes a number of catalytic sensing elements in which a platinum wire is coated with catalytically activated ceramic materials. The platinum wire is heated to a high temperature. In the presence of combustible gas, the platinum wire raises the temperature. The positive coefficient of temperature resistance of the platinum wire which increases the resistance of the wire therefore can be used as a signal to detect combustible gas. This method has been in use for the last quarter century but has a disadvantage in that the element will burn out in high gas concentrations. The gas to air mixture has to be in the right combustible mixture. In the upper explosive region the sensor is inactivated because of a lack of oxygen. This weakness endangers nearby life and properties. In addition, catalytic activity decreases in the presence of certain impurities such as low concentrations of H.sub.2 S. In addition, it will not detect gas in low ppm range.
In recent years, a semiconductor gas sensor generated great interest. This sensor, in general, consists of various ceramic material. In the processing of this ceramic, a non-ceramic material is added which evaporated when heated, thereupon creating a porous sintered structure in the ceramic. In the presence of certain air impurities, the gas molecules are absorbed by this sintered ceramic which changes its electroconductivity. This method obtains very interesting results as far as obtaining high sensitivity to gas goes. But in practical application it cannot offer any accuracy in quantitiative determination of the gases. It is also without any specificity to any gases So accordingly, it cannot be used as a monitoring device. In addition, prior methods of gas detection include chemical tapes, chemical gels, wet chemical instruments, and other devices. All of these are based upon different theories or principals of operation than electrolytic cell sensor.
Unfortunately, all of the prior art detectors have one or more of the following disadvantages:
1. Some of them burn out when exposed to high concentrations of gases;
2. Some of them are poisoned and thus rendered useless by toxic gases;
3. Some of them are incapable of measuring low concentrations of impurities or high concentrations of impurities or both;
4. Some of them have an extremely short life;
5. Some of them are effected by differences in temperature or attitude;
6. Some of them require a vacuum or other pump to circulate the gas sample;
7. Some of them require five, ten or even sixty minutes to respond.
The prior art, such as the Bott et al. patent 3,865,550, discloses a semi-conducting element whose electrical conductivity is dependent upon the concentration of the gas in the atmosphere. Prior to applicant's original application, the prior art does not disclose any sensor which caused the dissociation of the gases to be measured into charged species such as ions and complex ions.